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Outcome measures: Fasting plasma or serum from each subject was analysed for folate, vitamin B12 and homocysteine concentration. A semi-quantitative Food Frequency Questionnaire was completed by a subset of subjects from each group to determine methionine intake.

Results: The two meat eating groups consumed significantly greater levels of methionine (P<0.001). There was no clear trend in plasma folate status between groups, however the plasma vitamin B12 concentration decreased progressively from the high-meat-eating group to vegans (P<0.05). An inverse trend was observed with plasma homocysteine concentration, with vegans showing the highest levels and high meat eaters the lowest (P<0.05).

Conclusions: Dietary methionine intake has no observable effect on plasma homocysteine concentration. In habitual diets, where folate intake is adequate, lowered vitamin B12 intake from animal foods leads to depleted plasma vitamin B12 concentration with a concomitant increase in homocysteine concentration. The suggested mechanism is the failure to transfer a methyl group from methyl tetrahydrofolate by vitamin B12 in the remethylation of homocysteine to methionine.

Sponsorship: The study was funded by the Meat Research Corporation of Australia.

Author information

Affiliations

Department of Food Science, RMIT University, Melbourne, Australia

NJ Mann

, D Li

, AJ Sinclair

, AK Wilson

& FD Kelly

Department of Cardiovascular Medicine, Centre for Thrombosis and Vascular Research, University of New South Wales, Sydney, Australia

NPB Dudman

& XW Guo

Centre for Program Evaluation, The University of Melbourne, Melbourne, Australia

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Contributions

Guarantor: AJ Sinclair.

Contributorship: NJM, DL, AJS and NPBD initiated the study. NJM prepared the first draft of paper, and helped in data collection. DL finalized the draft of paper, collected data and helped in laboratory assays. AJS selected the study site, supervised the project, and secured the funding. XWG did part of the laboratory assays. GRE did the statistical analysis. AKW and FDK did the dietary data analysis. All authors contributed to drafts of the paper.

Corresponding author

Correspondence to NJ Mann.

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